JPS6221867B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention is a novel Si ₃ N ₄ −
The present invention relates to a C-based amorphous material and a method for producing the same. Recently, silicon nitride (Si ₃ N ₄ ) has attracted attention as a high-temperature structural material and an electrical insulating material. The present inventors first developed ultra-hard silicon nitride, which is resistant to thermal shock and has a size suitable for industrial use, using an inexpensive chemical vapor deposition (CVD) process.
Succeeded in synthesizing it by the method, and filed a patent application in 1982
(Japanese Unexamined Patent Publication No. 52-96999), but this time we succeeded in obtaining an excellent new Si ₃ N ₄ --C-based amorphous material whose properties are completely different in some respects. The Si ₃ N ₄ disclosed in Japanese Patent Application No. 51-2468 is useful as a high-temperature material because it has a small coefficient of thermal expansion, excellent thermal shock resistance, and high hardness not only at low temperatures but also at high temperatures. Furthermore, since it has extremely high electrical resistance, it is also useful in the electrical and electronic industries as an electrical insulating material. However, if electrical conductivity can be imparted to the above-mentioned materials, a wide range of applications can be expected as high-temperature electrical materials and high-hardness electrical materials. The present invention provides Si ₃ N ₄ that maintains the excellent thermal and mechanical properties of the above materials and has electrical conductivity. The Si ₃ N ₄ -C-based amorphous material of the present invention contains amorphous Si ₃ N ₄ and carbon obtained by simultaneous precipitation using a chemical vapor deposition method, and has an electrical conductivity σ=σ ₀ exp (−
0.02 to 0.06 electron volt/2kT). Here, σ ₀ is the proportionality constant, k is the Boltzmann constant, T is the absolute temperature, and E is the energy level of the valence body of amorphous carbon in the Si ₃ N ₄ -C-based amorphous material and the conductor. The energy gap that exists between the energy level of E=0.02~
It shows a value determined by the composition of the Si ₃ N ₄ --C-based amorphous material within a range of 0.06 eV. The proportionality constant σ ₀ is obtained as follows. Electrical conductivity σ at temperature T (K) is σ (T),
Electrical conductivity σ at 273K (0℃) is σ(273)
Then, σ(T)=σ ₀ exp(−E/2kT) ……(1) σ(273)=σ ₀ exp(−E/2k×273) ……(2) (1)÷(2) Than When (3) is transformed, Comparing equations (1) and (4), we get

[Formula] becomes. For example, when E=0.06eV, k=8.62×
Substituting 10 ^-5 eV/k, σ ₀ = 3.58×σ (273)
becomes. Similarly, when E=0.02eV, σ ₀ =
It becomes 1.53×σ(273). The value of electrical conductivity σ is approximately 10 ^-1 to ^{10 -3} Ω ^-1 cm at room temperature.
^-1 . Density is 2.6 to 3.0 g/cm ³ , thermal conductivity is 0.004 to 0.010 cal/cm・sec・℃ at room temperature, specific heat is about 0.16 cal/g・℃ at room temperature, thermal diffusivity is 0.010 to 0.010 at room temperature
0.022 cm ² /sec, and microvits hardness is 2500 to 3500 Kg/mm ² at room temperature when loaded with 100 g. According to the method of the present invention, Japanese Patent Application No. 51-2468
It was possible to obtain an Si ₃ N ₄ -C-based amorphous material with the same large size and large size as Si ₃ N ₄ . The electrical resistance of the material of the present invention can be determined, for example, by
Compared to Si ₃ N ₄ in No. 2468, it was possible to reduce the amount by 10 ¹² times at room temperature, making it extremely conductive. An example is shown in FIG. The figure shows the case where the synthesis temperature is 1300℃. The marks in the figure are when the propane gas flow rate is 0cm ³ /min, the 〇 marks are when the flow rate is 10cm ³ /min, the ■ marks are when the flow rate is 25cm ³ /min, and the □
The mark is for 40cm ³ /min, ▲ is for 70cm ³ /min, △
The mark indicates the case of 100cm ³ /min. Furthermore, the temperature coefficient of electrical resistance has become extremely small. Furthermore, the electrical conductivity of other typical ceramics is compared with that in FIG. The material of the present invention exhibits an electrical conductivity approximately intermediate between that of other insulating ceramics and conductive ceramics. "Journal of Less-Common Metals"
Vol 37, (1974) p317-329, "Chemical Vapor Deposition in the System
Silicon−Carbon and Silicon−Carbon−
According to Nitrogen, the raw materials are SiCl ₄ and CCl ₄ .
A gaseous mixture of _N2 and _H2 is reacted in the gas phase at a temperature in the range of 1100-1300℃ to form _{amorphous Si3N4} and crystalline (β type)
A mixture of SiC is produced, but the electrical properties or other physical and chemical properties of this mixture are not described. In addition, Si-C-
N-based materials are conventionally known, but all of them are mixtures of crystalline Si ₃ N ₄ and crystalline SiC. According to US Pat. No. 3,926,857, crystalline
By adding 10-20% by weight of colloidal carbon _{to Si3N4} , mixing this and heat-treating at 1300-1450℃ for 15-20 hours to change the colloidal carbon to SiC,
A Si ₃ N ₄ -SiC material containing 16 to 29.5 volume % of SiC is obtained, and its electrical resistance is 2.5 to 140 Ωcm. Also,
The paper “Preparation, Microstructure, and
According to ``Mechanical Properties of Silicon Nitride'', the creep strength of crystalline Si <sub>3</sub> N <sub>4</sub> at 1200° C. was significantly improved by mixing 5% by weight of crystalline SiC with crystalline Si <sub>3</sub> N <sub>4</sub> . Also,
"Journal of American Ceramic Society"
The paper “Effect of Microstructure on Strength of
According to ``Si ₃ N ₄ −SiC Composite System'', a mixture of crystalline Si ₃ N ₄ and 20% by volume of crystalline SiC
The high temperature strength at 1400°C is twice that of crystalline Si ₃ N ₄ . However, as can be seen from the descriptions in these publications, no mixture of amorphous Si ₃ N ₄ and carbon has ever been produced, and its various properties, especially its electrical properties, are completely unknown. Not yet. The Si ₃ N ₄ -C-based amorphous material of the present invention is produced by chemical vapor deposition using a silicon deposition source gas, a nitrogen deposition source gas, and a carbon deposition source gas in addition to H ₂ at a synthesis temperature of 1100 to
1300℃, total pressure in the furnace 30~70mmHg (30~70Torr)
It is synthesized by depositing an Si ₃ N ₄ --C-based amorphous material on a substrate. Prior to the synthesis reaction, the temperature inside the furnace is approximately 0.001mmHg.
It is preferred to degas the substrate by applying a vacuum of (10 ⁻³ Torr) and heating the substrate to 700-800° C. for several minutes. Next, the inside of the furnace is made into a hydrogen atmosphere, the substrate is heated to a predetermined temperature, and C ₃ H ₈ or CCl ₄ gas, NH ₃ gas, SiCl ₄ + H ₂
It is preferable to charge the gases into the furnace in this order. The substrate may be any material as long as it can withstand the deposition temperature and is corrosion resistant to atmospheric gases. Usually graphite is used. Produced by adjusting the flow rate of carbon deposition source gas
The carbon content of the Si ₃ N ₄ -C-based amorphous material is adjusted. In one experimental example of the present invention, patent application No. 51-
Using a device almost similar to the device in No. 2468, propane gas was used as the carbon deposition source gas, and its flow rate was
The carbon content was adjusted to less than 100 cm ³ /min to about 10% by weight or less. Although it was possible to increase the content to more than about 10% by weight, this is not preferable because cracks will occur. Regarding the operation of the method of the present invention, please refer to the following patent application
The method of operating the device of No. 2468 may optionally be used. In the present invention, appropriate and inappropriate ranges and suitable ranges of manufacturing conditions are shown in FIGS. 3 to 5. When the Si ₃ N ₄ --C-based amorphous material of the present invention is heated in air at about 300° C. or higher, C is oxidized and escapes as a gas, leaving behind a porous substance. This material has low electrical conductivity and is amorphous. By adjusting the degree of heating, electrical conductivity and porosity are adjusted. By impregnating the pores with an abrasive, Teflon resin, insulating oil, etc., the mechanical and electrical properties of amorphous Si ₃ N ₄ can be improved or modified. It can also be used as a microfilter without impregnation. The Si ₃ N ₄ --C-based amorphous material of the present invention can be used in the following fields by taking advantage of the excellent electrical properties and high-temperature properties described above. 1. As a coating material (a) By coating the surface of a substrate made of any material, it imparts conductivity even to a substrate made of an insulating material. (b) Prevent the generation of static electricity by coating the surface of the insulator. (c) By coating the surface of any material, it prevents reactions with high-temperature corrosive gases, chemicals, and molten metals (for example, crucibles, chemical plants, rocket nozzles, etc.). (d) Prevent wear and high-temperature seizure by coating the surfaces of mechanical parts that require wear resistance (e.g. bearings, gears, etc.). 2. As a block material (e) For heating elements that require light weight and high hardness, such as recording thermal pens. (f) For the recording needle of electrostatic printing equipment. (g) For high temperature filaments. (H) For high temperature heating elements. (li) As a microfilter by heat treatment in an oxidizing atmosphere. The invention will now be explained in more detail with reference to examples. Example 1 Using almost the same apparatus as shown in Japanese Patent Application No. 51-2468, a plate-shaped substrate made of artificial graphite was heated to 1300°C, and propane gas was added to it at 70 cm ³ /min and ammonia gas was added at 60 cm ³ /min. Hydrogen gas containing saturated silicon tetrachloride vapor at 20° C. was charged into the reactor at a flow rate of 700 cm ³ /min using a double tube. Note that ammonia gas was discharged from the inner tube of the double tube, and other gases were discharged from the outer tube. The pressure inside the reactor at that time was 30 mmHg. After flowing the gas for 6 hours, the current was turned off and the substrate was cooled. When the substrate inside was taken out, a black plate-like Si ₃ N ₄ -C amorphous material with a thickness of 1.8 mm was obtained on the surface of the substrate. Ta. The deposition rate at this time was 0.3 mm/hour. The properties of this material were measured and were as follows. Density 2.95g/cm ³ , Si/N 0.67, carbon concentration 2% by weight, hardness 2700Kg/mm ² (100g load), electrical resistance 32Ωcm (200℃), 20Ωcm (900℃), thermal conductivity
0.0085 cal/cm・sec・℃, specific heat 1.7 cal/g・℃, thermal diffusivity 0.017cm ² /sec. According to X-ray diffraction, no SiC was present. Example 2 A Si ₃ N ₄ --C-based amorphous material was produced using the same apparatus as in Example 1 and performing the same operations. Manufacturing conditions are substrate temperature 1300℃, ammonia gas flow rate.
60cm ³ /min, propane gas flow rate 100cm ³ /min, hydrogen gas containing saturated silicon tetrachloride vapor at 20℃ 700cm ^{3 /} min
The pressure inside the reactor was 70 mmHg. A black plate with a thickness of 3 mm was formed on the surface of the substrate after 6 hours of reaction time.
A Si ₃ N ₄ -C based amorphous material was obtained. The deposition rate at this time was 0.5 mm/hour. The properties of this material were measured and were as follows. Density 2.8g/cm ³ ,
Si/N0.67, carbon concentration 10% by weight, hardness 2600Kg/mm ²
(100 load), electrical resistance 20Ωcm (200℃), 15Ωcm
(900℃), thermal conductivity 0.0065cal/cm・sec・℃, specific heat
1.7cal/g・℃, thermal diffusivity 0.013cm ² /sec. Example 3 When the Si ₃ N ₄ -C amorphous material obtained in Example 1 was heated in air at 400°C for 6 hours, the electrical resistance was 3 × 10 ² Ωcm at 400°C and 2 at 1000°C. ×10 ⁵
I became Ωcm. However, properties other than electrical resistance, such as density and thermal conductivity, did not change at all. Example 4 Using the same apparatus as in Example 1, artificial graphite molded into a crucible shape was used as the heating element, commercially available sintered silicon nitride was placed in it, and the sintered silicon nitride was placed on top of the sintered silicon nitride.
A Si ₃ N ₄ -C based amorphous material was coated. The coating conditions were as follows. Base temperature 1300
℃, ammonia gas flow rate 60cm ³ /min, propane gas flow rate 40cm ³ /min, hydrogen gas containing saturated silicon tetrachloride vapor at 20℃ 700cm ³ /min, pressure inside the reactor 30mmHg,
Reaction time: 10 minutes. Black color on sintered silicon nitride surface
A Si ₃ N ₄ -C based amorphous coating was obtained with a film thickness of 50 μm.
The carbon content was 0.6% by weight. The adhesion between the Si ₃ N ₄ -C-based amorphous coating and the commercially available sintered silicon nitride was extremely strong, and did not peel off even after rapid cooling from 1300°C.

[Brief explanation of the drawing]

Figure 1 is a characteristic diagram showing the electrical conductivity at high temperatures of the Si ₃ N ₄ -C based amorphous material of the present invention using the propane gas flow rate during synthesis as a parameter, and Figure 2 is a characteristic diagram of the present invention.
Characteristic diagrams that compare and show the relationship between electrical conductivity and temperature of Si ₃ N ₄ -C-based amorphous materials and other ceramic materials. Figures 3 to 5 show appropriate, inappropriate, or suitable manufacturing conditions. It is a characteristic diagram.

Claims (1)

[Claims] 1 Contains amorphous Si ₃ N ₄ and carbon obtained by co-precipitating by chemical vapor deposition method, and has electrical conductivity σ=σ ₀ exp (-E/2kT) (however, σ ₀ is the proportionality constant, k is the Boltzmann constant, T is the absolute temperature, and E is the energy level of the valence body of amorphous carbon in the Si ₃ N ₄ -C-based amorphous material and the energy level of the conductor. The energy gap that exists between E=0.02~
1. A Si ₃ N ₄ -C amorphous material having a value determined by the composition of the Si ₃ N ₄ -C amorphous material within a range of 0.06 eV. 2. The _Si3N4 -C-based amorphous material according to claim 1, wherein the content of 2C is about 10% by weight _or less. 3 Contains amorphous Si ₃ N ₄ and carbon obtained by co-precipitating by chemical vapor deposition method, and has electrical conductivity σ = σ ₀ exp (-E/2kT) (where σ ₀ is a proportionality constant, k is the Boltzmann constant, T is the absolute temperature, and E exists between the energy level of the valence body of amorphous carbon in the Si ₃ N ₄ -C-based amorphous material and the energy level of the conductor. Energy gap, E=0.02～
_The Si ₃ N ₄ -C amorphous material is heated in air at a _temperature of about 300°C or above. Si ₃ N ₄ characterized by increased electrical resistance by heating at high temperatures
-C-based amorphous material. 4 By chemical vapor deposition method, silicon deposition source gas,
Add carbon deposition source gas to nitrogen deposition source gas and _H2 , synthesis temperature 1100~1300℃, total furnace pressure 30~70mm
By reacting under Hg precipitation conditions, Si ₃ N ₄ -C is deposited on the substrate.
characterized by depositing amorphous material
A method for producing a Si ₃ N ₄ -C-based amorphous material.